Controllable coolant pump

ABSTRACT

A controllable coolant pump for a coolant circuit of an internal combustion engine. The coolant pump has a hollow bearing shaft which is supported in a bearing sleeve, carries a drive wheel at one end, and is permanently connected to an impeller at its opposite end, the impeller having a stop surface at the end face thereof. The space between the stop surface and the impeller forms the pumping cross section for a coolant. A piston that can be axially displaced by an actuation unit is disposed in the hollow bearing shaft and provided at its outer end with a guide plate having a collar facing the impeller for completely or partially closing the pumping cross section in accordance with the position of the piston. The coolant pump has a second actuation unit, and the piston can be displaced by the first or second actuation unit.

The present invention relates to a controllable coolant pump for a coolant circuit of an internal combustion engine. The coolant pump has a hollow bearing shaft which is supported in a bearing sleeve, carries a drive wheel at one end, and is permanently connected to an impeller at its opposite end, the impeller having a stop surface at the end face thereof. The space between the stop surface and the impeller forms the pumping cross section for a coolant. A piston that can be axially displaced by an actuation unit is disposed in the hollow bearing shaft and provided at its outer end with a guide plate having a collar for completely or partially closing the pumping cross section in accordance with the position of the piston.

BACKGROUND

Water-cooled engines have become predominant in the field of internal combustion engines. In such engines, cooling water is pumped by a coolant pump in a closed loop through cooling passages in the region of the cylinders in order to cool the internal combustion engine, and is then conveyed to an air/water radiator, where the heated water is cooled down by the relative wind generated by the motion of the vehicle. The pump required to circulate the cooling water is typically connected by a belt to a pulley of the crankshaft of the internal combustion engine.

Since the coolant pump is directly coupled to the crankshaft in this way, the rotational speed of the pump is dependent on the rotational speed of the internal combustion engine. As a result, in the high speed range of the internal combustion engine, the pump delivers a correspondingly high flow rate, which exceeds that required for cooling. However, during cold starting of the internal combustion engine, the problem arises that coolant is immediately circulated through the cooling passages, thereby hindering the heating of the combustion chambers and delaying the attainment of an optimum operating temperature.

A controllable coolant pump of the aforementioned type is known from German Patent Application DE 2008 046 424 A1. In this coolant pump, a guide plate having a contour corresponding to the impeller is disposed between the impeller and a stop surface, the guide plate being guided by axial webs connecting the impeller and the stop surface, and being axially displaceable by an actuation unit by means of a piston placed within the hollow shaft.

The guide plate is provided at its outer edge with a collar by which it may cover an annular channel of a pump housing depending on its position between the impeller and the stop surface. Thus, the annular channel can be fully or partially covered, so that no cooling liquid is pumped through the cooling passages. The axial positioning of the piston is accomplished by means of a magnet.

If an electrical actuation unit including a motor and a downstream transmission mechanism is used in such a controllable coolant pump, supply to a component of the actuation unit in most cases results in self-locking, making it impossible to ensure return to the initial position in the event of a failure of the electric motor or a transmission component. However, this condition is critical for the internal combustion engine because the pumping cross section is closed when the piston is in the extended position, so that no coolant is pumped through the cooling passages. Therefore, in the event of failure of a component of the actuation unit, there is a risk of overheating of the internal combustion engine.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a controllable coolant pump that has a higher fault tolerance.

The present invention provides that the controllable coolant pump has a second actuation unit and in that the piston can be displaced by the first or second actuation unit.

The present invention is based on the realization that the risk of overheating of the internal combustion engine can be significantly reduced by providing a second, separate actuation unit as an actuator. In the event of a failure of the first actuation unit, the second actuation unit ensures reliable return to an initial or normal position in which the pumping cross section for the coolant is open. Thus, the required cooling of the internal combustion engine is ensured even if the first actuation unit fails.

Particularly high functional reliability is achieved when the controllable coolant pump according to the present invention has a lever which is pivotable about an axis of rotation, the lever being pivotable by the first or second actuation unit. Preferably, upon actuation, a lead screw is axially displaced by an actuation unit, the lead screw pivoting the lever in the process. Since the lever contacts the piston, pivoting of the lever by an actuation unit causes a movement, in particular a displacement, of the piston, thereby adjusting the pumping cross section.

In an embodiment of the controllable coolant pump according to the present invention, the first or second actuation unit defines the axis of rotation of the lever. The lever, in particular an end of the lever, may in particular be disposed at a lead screw connected to an electric motor. Thus, the lever is pivoted about a non-stationary axis of rotation. The lever and the actuation unit are connected to each other in articulated fashion.

In a particularly reliable embodiment of the coolant pump according to the present invention, the piston and the lever have a common mounting point, which is located between a contact point between the lever and the first or second actuation unit and a contact point between the lever and the respective other actuation unit. Thus, the piston can be actuated by either of the two actuation units.

In an alternative embodiment of the coolant pump according to the present invention, the piston is disposed distal from the pivot point, and the first and second actuation units are disposed proximal to the pivot point and are preferably spaced apart. Alternatively, the two actuation units may also be disposed at the same point of the lever.

A particularly high fault tolerance can be achieved for the coolant pump according to the present invention when one of the two actuation units is operable to open the pumping cross section of the impeller in the event that the respective other actuation unit fails. A potential failure of an actuation unit may be detected by resistance measurement or by a position sensor. The position sensor may, for example, detect the position of a lead screw of the first or second actuation unit, thereby making it possible to infer the position of the lever, and thus the position of the piston. Additionally or alternatively, the sensor may detect the position of the piston in the axial direction. If a discrepancy is detected between the actual position and the desired position of the piston, the respective other actuation unit can be activated to displace the piston by pivoting the lever.

A particularly simple way of displacing the piston and thereby precisely setting the desired pumping cross section is obtained when the first and/or second actuation unit includes an axially displaceable lead screw whose end portion contacts the lever or is coupled thereto. The lead screw may also be coupled to a lead screw nut driven by an electric motor, possibly with speed conversion being provided between a pinion of an output shaft of the electric motor and a lead screw nut.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention are illustrated in the drawings and described in more detail below. In the drawing,

FIG. 1 shows in a cross-sectional view a conventional controllable coolant pump;

FIG. 2 shows a first exemplary embodiment of a controllable coolant pump according to the present invention;

FIG. 3 shows the coolant pump of FIG. 2 in the extended position;

FIG. 4 shows the coolant pump of FIGS. 2 and 3 after a failure of an actuation unit;

FIG. 5 shows a second exemplary embodiment of a controllable coolant pump according to the present invention;

FIG. 6 shows the coolant pump of FIG. 5 in the extended position; and

FIG. 7 shows the coolant pump of FIGS. 5 and 6 after a failure of an actuating element.

DETAILED DESCRIPTION

The design and operation of a controllable coolant pump is described with reference to FIG. 1. FIG. 1 is a cross-sectional view showing a conventional coolant pump 1 including a bearing shaft 3 which is supported in a pump housing 2, carries a drive wheel 4 at one end, and is permanently connected to an impeller 5 at its opposite end Impeller 5 has a stop surface 6 at the end face thereof. The space between stop surface 6 and impeller 5 forms the pumping cross section for a coolant, in particular cooling water. A piston 7 that can be axially displaced by an actuation unit (not shown) is disposed in hollow bearing shaft 3 and provided at its outer end with a guide plate 8 having a collar 9 for completely or partially closing the pumping cross section in accordance with the position of piston 7.

When piston 7 is in the position shown in FIG. 1, the pumping cross section between arrows 10 is cleared. When piston 7 is displaced in a direction toward stop surface 6 by an electromechanical actuating element, the pumping cross section is reduced or completely closed. This allows control of the coolant flow pumped into cooling passages of an internal combustion engine.

Upon starting of the internal combustion engine, the drive wheel 4 coupled to the crankshaft is set in rotation. Accordingly, bearing shaft 3 rotates impeller 5, thereby pumping coolant. However, during cold starting, pumping of coolant it is initially not desired, so that piston 7 is displaced in a direction toward impeller 5, thereby closing the pumping cross section. In this condition, no coolant is pumped, which speeds up the heating of the engine. During normal operation, the pumping cross section is partially or completely cleared, so that the coolant is pumped through cooling passages of the internal combustion engine, thus cooling the engine.

The following exemplary embodiments of coolant pumps are in principle designed similar to the one shown in FIG. 1. However, for the sake of clarity, individual components which are irrelevant to the understanding of the present invention are not shown in the respective drawings. In particular, the drive wheel, the impeller, and the guide plate have been omitted for the sake of simplicity.

FIG. 2 shows components of a coolant pump whose piston 11 is axially displaceable. Not shown in FIG. 2 is the bearing sleeve within which piston 11 is movable. The coolant pump includes a first actuation unit 12 and a second actuation unit 13, each actuation unit 12, 13 having an electric motor M with a lead screw nut 27 (shown schematically in actuation unit 12) and an axially displaceable lead screw 14, 15. FIG. 2 shows the actuator of the cooling pump in a normal position. The free end of lead screw 14 is articulated to a lever 16. The contact point between lever 16 and the free end of lead screw 14 defines an axis of rotation 17 for lever 16. Similarly, the free end of lead screw 15 of second actuation unit 13 is articulated to the other end of lever 16.

Upon actuation of first actuation unit 12, an output shaft of the electric motor, and thus also lead screw 14, is set in rotation, thereby increasing or decreasing the length of the projection portion of lead screw 14. Movement of lead screw 14 causes lever 16 to rotate about an axis of rotation 18 in the region of attachment of the lever to the free end of lead screw 15. Conversely, when lead screw 15 is axially moved, lever 16 rotates about axis of rotation 17. Rotation or pivoting of lever 16 positively displaces pivots piston 11 axially.

FIG. 3 shows the condition when lead screw 15 of second actuation unit 13 is fully extended. In this condition, piston 11 has been displaced by a distance X with respect to the normal position shown in FIG. 2.

Actuation unit 13 functions as the main actuator for controlling the axial position of piston 11. In contrast, actuation unit 12 is not needed during normal operation. A sensor 19, schematically shown in FIG. 3, is associated with piston 11 to detect the instantaneous position of piston 11 in the axial direction. Sensor 19 is a non-contact sensor, such as, for example, a magnetic field sensor or a Hall effect sensor or a capacitive sensor.

FIG. 4 illustrates the unlikely, but not impossible event of a failure of actuation unit 13. When actuation unit 13 fails, piston 11 cannot be retracted by lead screw 15. In this condition, piston 11 is completely or nearly completely extended. Accordingly, the pumping cross section for the coolant between the stop surface and the impeller is closed or at least nearly closed. Since in this condition, no coolant can be pumped into cooling passages, there is a risk of undue heating of the internal combustion engine, which may lead to permanent damage. In order to prevent damage to the internal combustion engine, lead screw 14 of actuation unit 12 can be retracted, as shown in FIG. 4. To this end, lead screw 14 is moved by the electric motor into the housing of actuation unit 12, whereby the end of lever 16 that is coupled to lead screw 14 is pivoted about axis of rotation 18 (counterclockwise in the view of FIG. 4). Since piston 11 is articulated to lever 16, this pivoting movement of lever 16 causes piston 11 to be retracted (to the left in the view of FIG. 4). In this way, the pumping cross section between the stop surface and the impeller is cleared, allowing the coolant to flow through the cooling passages again, thereby preventing the coolant pump from failure. Upon failure of an actuating element, a failure message may be output, allowing the user to arrange for repair or replacement. In the meantime, the operation of the coolant pump is fully maintained by the second actuation unit. Tests have shown that the probability of failure of such a coolant pump is a factor of 10 lower than that of a conventional cooling pump.

FIGS. 5 through 7 illustrate a second exemplary embodiment of the actuation units of a coolant pump.

A lever 20 is articulated by one end 21 to the lead screw 23 of an actuation unit 22. The articulated joint at the end 21 of lever 20 also acts as a pivot point for lever 20 when a second actuation unit 24 having a lead screw 25 is operated.

FIG. 6 shows the actuation units of FIG. 5 in the extended position. Upon actuation of actuation unit 24, lead screw 25 is extended. Accordingly, lever 20 pivots about its end 21, which serves as a pivot point. In the view of FIG. 6, a clockwise rotation is performed. Near its free end, lever 20 contacts piston 11, which is positively displaced axially (to the right in the view of FIG. 6), thereby changing the pumping cross section between the stop surface and the impeller. Displacement of the piston in the direction shown in FIG. 6 reduces the pumping cross section.

In the event that actuation unit 24 fails in the position shown in FIG. 6, the other actuation unit 22 can be operated as an auxiliary actuator to return piston 11 to its normal position. To this end, lead screw 23 is extended as shown in FIG. 7, so that lever 20 pivots about the point of contact 26 with lead screw 25, while sliding over the edge of lead screw 25. As a result, piston 11, which is coupled to lever 20, is retracted (to the left in the view of FIG. 7), thereby clearing the pumping cross section.

LIST OF REFERENCE NUMERALS

-   1 coolant pump -   2 pump housing -   3 bearing shaft -   4 drive wheel -   5 impeller -   6 stop surface -   7 piston -   8 guide plate -   9 collar -   10 arrow -   11 piston -   12 actuation unit -   13 actuation unit -   14 lead screw -   15 lead screw -   16 lever -   17 axis of rotation -   18 axis of rotation -   19 sensor -   20 lever -   21 end -   22 actuation unit -   23 lead screw -   24 actuation unit -   25 lead screw -   26 contact point -   27 lead screw nut -   M motor 

1-9. (canceled)
 10. A controllable coolant pump for a coolant circuit of an internal combustion engine, the coolant pump comprising: a hollow bearing shaft supported in a bearing sleeve and carrying a drive wheel at one end and permanently connected to an impeller at an opposite end, the impeller having a stop surface at an end face, a space between the stop surface and the impeller forming a pumping cross section for a coolant; a piston axially disposed in the hollow bearing shaft and provided at an outer end with a guide plate having a collar facing the impeller for completely or partially closing the pumping cross section in accordance with the position of the piston; and a first and a second actuation unit, the piston displaceable by the first or second actuation unit.
 11. The controllable coolant pump as recited in claim 10 further comprising a lever pivotable about an axis of rotation, the lever being pivotable by the first or second actuation unit.
 12. The controllable coolant pump as recited in claim 10 wherein the first or second actuation unit defines an axis of rotation of the lever.
 13. The controllable coolant pump as recited in claim 11 wherein the piston and the lever have a common mounting point located between a contact point between the lever and the first or second actuation unit and a second contact point between the lever and the respective other of the first and second actuation units.
 14. The controllable coolant pump as recited in claim 11 wherein the piston is disposed distal from a pivot point of the lever, the first and second actuation units being disposed proximal to the pivot point.
 15. The controllable coolant pump as recited in claim 14 wherein the first and second actuation units are spaced apart.
 16. The controllable coolant pump as recited in claim 10 wherein one of the first and second actuation units is operable to open the pumping cross section of the impeller in the event that the respective other actuation unit fails.
 17. The controllable coolant pump as recited in claim 11 wherein the first and/or second actuation unit includes an axially displaceable lead screw having an end portion contacting or coupled to the lever.
 18. The controllable coolant pump as recited in claim 17 wherein the lead screw is coupled to a lead screw nut driven by an electric motor.
 19. The controllable coolant pump as recited in claim 10 further comprising a sensor for detecting the axial position of the piston. 